1. Field of the Invention
This invention relates to rotating machines, especially high-speed rotating machines, in which there is a rotating shaft with a rotor or other rotating member attached to it, and more especially in which the rotor is attached to the end of the shaft.
Most of the attachments for rotors or wheels on rotating shafts are by means of a hole through the center of the rotor with keys or other rotary driving means interconnecting them, and the rotor is held against a shaft shoulder by means of a screw or nut. In some instances, where it is objectionable to have a hole in the center of the rotor, the rotor is held on the shaft by a facing flange on the shaft with screws passing through holes in the marginal portions of the flange, usually threaded into the rotor.
In some other instances the rotor is attached by means of matching gear teeth called a curvic coupling, one member of the matched pair being on the wheel and the other on the shaft. Such a coupling is illustrated in FIG. 2 of the patent to Wildhaber, U.S. Pat. No. 2,429,284, issued Oct. 21, 1947.
Such an attachment of a rotor to a shaft, whatever its form, must have adequate driving strength and must maintain concentric and angular alignment between the rotor and shaft.
The application in which such rotor and shaft are used may subject the two to differing temperatures. Also, the rotor is more highly stressed at the center bore than in other portions of the rotor, and this plus the temperature difference changes the relative fit of the bore in the rotor about the shaft, and tends to leave the rotor free to move radially somewhat, thereby causing the assembly to become unbalanced.
The above mentioned high tangential stress at the bore of the rotor, because of Poisson's ratio effects, causes a corresponding axial shrinkage of the rotor adjacent the bore, so that the bolt or nut clamping the rotor on the shaft has a tendency to be loose during high speed rotation because of this shrinkage.
2. Description of Prior Art
These problems are normally solved or attempted to be solved by having as tight fit as possible of the rotor bore on the shaft and by having keys on the shaft or splines on the shaft. In the case of the flanged attachment mentioned above, the flange attachment is assumed to stretch reasonably uniformly in all radial directions and thereby to maintain reasonably good axial alignment. However, there is nothing to ensure such uniformity of radial stretch nor positive maintainence of alignment of the axes.
Sometimes the attachment in the bore of the wheel is made with a shrink fit with the hope that after the rotor stretches, it will not be excessively loose. Such a joint on a shrink fit, or a taper fit, is often difficult to disassemble.
These radial fits also have another problem if there is slight angular (rotational) looseness -- they allow possible relative movement of the rotor on the shaft causing possible wear and fretting.